Once considered a no hoper, Bernie Sanders has brought the race for the Democratic nomination to life.

In a matter of weeks, buoyed by massive crowds wherever he speaks, the 73-year-old Brooklyn-born independent senator for the New England state of Vermont has gone from a fringe left-wing candidate to a powerful voice on the left who is making Hillary Clinton's campaign rather more difficult than she might have hoped.

In recent weeks her poll lead has shrunk dramatically. In New Hampshire the 38-point gap over Mr Sanders in May has fallen to eight points and in Iowa, over the same period, it has dwindled from 45pc to 19pc.

"He has come right out of the blue," said Andrew Preston, Professor of American history at Cambridge University. Unable to draw on the huge corporate donations that have helped Mrs Clinton, the self-declared unapologetic democratic socialist is surfing a tidal wave of left-wing grassroots support. While Mrs Clinton's contact with voters has been limited and carefully controlled, the same could not be said of Mr Sanders.

At the end of his hour-long oration to an audience of nearly 10,000 at a sports arena in Portland, Maine, he plunged into the audience - grasping hands and posing for selfies.

With the audience whooping in agreement, the atmosphere was part rally and part revivalist meeting, which had seen people arriving more that two hours ahead of the event to make sure they could get in.

From teens to voters in their 70s, the crowd had flocked there to hear a distinctly alternative message in which he rounded on the wealthiest in America.

"We are going to send a message to the billionaire class - you can't have it all," he said to resounding cheers. "You can't keep sending jobs to China, while millions of people in this country still need work."

From free student tuition to a comprehensive health system, Mr Sanders demanded sweeping changes in America, with the bill being sent to the wealthiest in the country.

Time and again he rounded on Wall Street, which he held responsible for many of the ills which beset America, especially after the banking crisis.

"If a bank is too big to fail, it is too big to exist," he said as he pledged a break-up of some of the largest financial institutions.

The meeting was typical of a barnstorming campaign that has drawn thousands to gatherings in Iowa, Wisconsin, Minneapolis and Denver.

"I think he is articulating what many Americans feel," said Ruth Becker (67), from Richmond, Maine. "I think things are skewed in the wrong way. Neither of the Clintons represent my politics."